CIKCULATION 



229 



the heart, and in contracting it pulls the walls of the ven- 

 tricles towards the septum ventriculi. 



3rd. The inmost layer is continuous with the outmost layer, 

 as it turns in at the apex. It may be considered as composed 

 of two parts 



(a i A layer of fibres running longitudinally along the inside 

 of each ventricle from the apex upwards to the auriculo- 

 ventricular ring. These fibres are raised into fleshy columns, 

 the eolumnse earnese. 



(b) A set of fibres, constituting the papillary muscles (fig. 

 109, P.M.), which, taking origin from the apical part of the 



FIG. 108. Cross Section through the Ventricles of the Heart looking towards 

 Auricles, to show the right Ventricle placed on the Central Core of the 

 left Ventricle. The cusps of the Auriculo ventricular Valves are also 

 shown. 



ventricles, extend freely upwards to terminate in a series of 

 tendinous cords (the ehopdse tendinese), which are inserted 

 partly into the auriculo- ventricular valves, presently to be 

 described, and partly into the auriculo-ventricular rings. 

 The papillary muscles are merely specially modified column* 

 carnete. In many cases, actual muscular processes extend 

 from the apex of the papillary muscles to the auriculo- 

 ventricular ring. 



In the left ventricle there are two papillary muscles, or 

 groups of papillary muscles, one in connection with the 

 anterior wall of the ventricle, and one in connection with the 

 posterior wall. 



